Auto focus system for reticle inspection

Abstract

Methods and apparatus relating to the inspection of photomasks are described. In an embodiment, an inspection tool may be automatically focused on a reticle utilizing various topographic mapping techniques. Other embodiments are also described.

The invention claimed is: 
     
       1. An apparatus comprising:
 an image capture device to capture one or more images of a reticle; and 
 a logic to focus a lens of the image capture device, wherein the logic is to focus the lens based on a topographical map comprising previously-stored height measurements Z of an upper surface of the reticle associated with X and Y coordinates of the reticle. 
 
     
     
       2. The apparatus of  claim 1 , further comprising logic to generate the topographical map. 
     
     
       3. The apparatus of  claim 2 , wherein the logic to generate the map generates the map based on one or more of: a confocal drill down process, a global mapping process, or a topographical map-following process. 
     
     
       4. The apparatus of  claim 2 , wherein the logic to generate the map updates the map in response to temperature variations. 
     
     
       5. The apparatus of  claim 1 , further comprising an intermediate field-plane mask comprising a plurality of holes. 
     
     
       6. The apparatus of  claim 1 , wherein the logic comprises at least one processor. 
     
     
       7. The apparatus of  claim 1 , further comprising a memory to store data corresponding to the reticle.